Method of improving the cutting speeds of carbon steels and ferrous alloys



Yrs... have United METHOD OF INIPROVDJG THE CUTTING SPEEDS OF CARBON STEELS AND FERROUS ALLOYS Alexandre Paudrat, Saint-Etienne, France No Drawing. Application February 11, 1955, Serial No. 487,695

This invention relates to the methods of improving on the one hand the cutting speeds of carbon steels and ferrous alloys, and on the other hand their resistance to wear as well as reducing their coefiicient of friction.

It is already known to improve the cutting speeds of ordinary carbon steels by adding sulfur to the molten steel during its preparation. As a rule, this sulfur addition takes place in the form of manganese sulfide or iron sulfide but, sometimes pure sulfur is employed. The quantity of sulfur thus added is calculated to provide a final sulfur content in the steel which ranges from 0.1% to 0.35%. In these known methods, however, sulfide inclusions occur in the steel which are noxious to the mechanical properties of the final product.

Now the method forming the subject-matter of this invention differs from the known processes in that (i) Sulfur is added in a much more moderate content;

(ii) Sulfur is not added during the preparation of the steel itself, but after full completion thereof; therefore, this sulfur addition may be termed a sulfur treatment;

(iii) Sulfur is incorporated with the steel mass at a predetermined temperature which is as close as possible to 1400 C.

(iv) Sulfur is added in its pure form.

A definite improvement of the machining possibilities and resistance to wear of the ferrous alloys is subordinated to the strict adherence to the four requirements listed hereinabove. According to a hypothesis expressed by the applicant, this improvement is attributable to the fixing of sulfur in its pure form to the intercrystalline boundaries.

Moreover, this invention affords a definite improvement of the cutting speeds and resistance to wear of all steels, including alloy steels, whereas prior methods are not applicable to steels containing, for example, chromium, nickel, molybdenum or tungsten.

The mechanical properties of the steels treated in accordance with the teachings of this invention are maintained inegrally. They display no brittleness, are homo geneous and may be normally tempered or case-hardened without difficulty. This is due to the fact that, according to this invention, the sulfur content subsequent to the treatment ranges from 0.035% to 0.55%, provided that the treated steel issues in clean state from the preparation stage; in other words, it is highly desirable that the steel itself does not contain any appreciable amount of sulfur, the latter being generally distributed in the form of sulfurous inclusions.

Sulfurizizzg treatment.-The steel to be sulfurized may be an ordinary carbon steel or an alloy steel. It should be clean preferably.

The addition of sulfur, in contradistinction with prior methods, takes place when the steel is fully prepared, i. e. in the ingot mold proper.

This sulfur addition procedure is based on the fact that it is necessary:

To reduce the temperature factor, usually responsible ates Patent for the formation of sulfide due to the thermal stirring of atoms,

To avoid any transfer or boiling of the molten mass, which tend to activate the sulfide formation;

To increase the instantaneity of the sulfur addition;

To reduce the setting time subsequent to the sulfur addition, as the influence exerted by this time is such that the smaller the ingots, the better the efficiency of the treatment.

The temperature at which the steel is cast into the ingot mold should be as close as possible to 1400 C., as already stated.

The quantity of sulfur to be added is relatively low, just sufiicient to coat the intercrystalline boundaries, i. e.:

60 grams of sulfur per hundred kilograms of steel, in the case of ordinary carbon steel;

50 grams of sulfur per hundred kilograms of steel, in the case of alloy steels.

The sulfur is added to the bottom of the ingot mold before casting of the metal and in the form of granules, of which the maximum dimension is between 40 and 50 With this procedure it is possible:

To nearly treble the cutting speeds of ordinary carbon steels in the half-hard and hard qualities;

To double the cutting speeds of alloy steels.

Moreover, the wear resistance is increased to a very substantial extent, and the coeificient of friction of these alloys is reduced while markedly improving their yielding properties.

The following examples illustrate the differences be tween the cutting speeds of an ordinary half-hard carbon steel and the same steel but treated in accordance with this invention.

The steel has been prepared in an electric arc furnace and subsequently poured into two different ingot molds. The above-described sulfurizing treatment is applied to one mold only.

I. Composition of untreated steel:

Tensile strength=82 kg.

First series of tests-Cutting speed=87.50 in. per minute A. Untreated steel.Number of parts machined between two subsequent tool sharpenings:

B. Steel treated according to this inventi0n.Number of parts machined between two subsequent tool sharpenings:

Ratio of tool holding times treated steel untreated steel Second series of tests.-Cutting speed=76.50 111. per minute A; Untreated .steel.--Number of parts machined between two subsequent tool sharpenings:

B. Steel treated according to this invention.Number of parts machined between two subsequent 'tool sharpenings: 256370223-305290500306 Ratio of tool holding times treated steel untreated steel There is a strong demand for steel castings having a relatively highwear resistance and good machining possibilities. This last property is sometimes ditficult to obtain due to the lack of homogeneity of ingot cast steel. It is the object of this invention to eliminate this difiiculty while incrementing the wear resistance of the castings.

Owing to the reasons set forth hereinabove, the sulfur treatment of the castings is effected as follows:

(1) Two thirds of the required quantity of sulfur by weight are uniformly distributed at the lowermost level of the casting. The sulfur employed is in the solid state and the granule size ranges from 20m 30 mm. in its greatest dimension.

The last third of sulfur is enclosed in one or more aluminum boxes, the granule size ranging in this case from to 20 mm. in its greatest dimension. The box or boxes are placed in a mold impression at aboutmid-height of the mold and supported by two or threealuminum wires stretched and fixed by one end in the opposite walls of the mold.

(2) The temperature at whichthe steel is'poured into the moldshould be as close as possible to 1400 C.

(3) The quantities of sulfur to be added are as follows: about 60 grams of sulfur for 100 kilograms of steel in the case of ordinary carbon steel; about grams of sulfur for 100 kilograms of steel in the case of alloy steel.

What I claim as new is:

1. In a method of improving the wear resistance and increasing the cutting speeds of carbon steels and ,alloy steels, the successive steps of preparing the metal, the cutting speed of which is to be increased, in the molten state introducing pure sulfur in solid form into the mold where the molten metal is to be cast, in an amount just sufiicient to coat the intercrystalline boundaries of the metal, and pouring the molten metal into the mold, the molten metal being at a temperature as close as possible to 1400 C.

2. A method according to claim 1, wherein the metal is carbon steel and the quantity of pure sulfur in solid form introduced into the mold at a temperature as close as possible to 1400 C. is about grams per kilograms of metal.

3. A methodaccording to claim 1, wherein the metal is alloy steel and the quantity of pure sulfur in solid form introduced into the mold at a temperature as close as pos sible to 1400 C. is about 50grams per 100 kilograms of metal.

References Cited in the file of this patent UNITED STATES PATENTS 1,959,758 Graham et a1. May 22, 1934 7 2,197,259 Nead Apr. 16, 1940 2,225,511 Soler Dec. 17, 1940 2,550,735 Tour May 1, 1951 FOREIGN PATENTS 350,919 Great Britain June 10, 1931 

1. IN A METHOD OF IMPROVING THE WEAR RESISTANCE AND INCREASING THE CUTTING SPEEDS OF CARBON STEELS AND ALLOY STEELS, THE SUCCESSIVE STEPS OF PREPARING THE METAL, THE CUTTING SPEED OF WHICH IS TO BE INCREASED, IN THE MOLTEN STATE INTRODUCING PURE SULFUR IN SOLID FORM INTO THE MOLD WHERE THE MOLTEN METAL IS TO BE CAST, IN AN AMOUNT JUST SUFFICIENT TO COAT THE INTERCRYSTALLINE BOUNDARIES OF THE METAL, AND POURING THE MOLTEN METAL INTO THE MOLD, THE MOLTEN METAL BEING AT A TEMPERATURE AS CLOSE AS POSSIBLE TO 1400*C. 